Automatic data capture has been a continuing and growing concern in the field of drafting and design automation since the start of computer aided design (CAD) systems. One longstanding problem has been how to maintain millions of large engineering drawings by converting the physical drawings into a CAD system for automatic data updating and how to avoid degradation of the file material. In one known type of large document automatic data capture system, two linear arrays of optical fibers are positioned in a scanning head parallel to each other and extending along the width of the scanning head which may, for example, be 1 meter wide. The scanner uses the optical fibers to pipe light from the scanned media to an electronic image sensor. The electronic signals are in digitized form and converted to a CAD formatted file and stored.
Optical fibers of either glass or plastic are made by continuous processes that employ feed-back arrangements to control the fiber diameter. These methods result in the diameter being held to plus or minus a few microns about a nominal dimension. The linear arrays of fibers for scanners are constructed so that the fibers touch each other as they are wrapped on a rotating drum. Because of the variation in diameter of the fiber, the nominal design spacing of fibers in the linear array varies across an array and from array to array. Due to this effect, it is state-of-the-art to have, for example, a tolerance of .+-.25 mm for a 1 meter wide array. This variation results in the array having a variable scanning resolution or fiber-to-fiber spacing that is not acceptable for precision scanners.
When the linear array is placed onto a flat bar for support, a second type of variation in the fiber position occurs. In manufacture of this type of assembly, the fibers are adhered to the support bar with epoxy resin. The location of the fibers from the bar is dependent on the thickness of the adhesive epoxy. Due to this effect, it is typical in the state-of-the-art to have a tolerance of .+-.1 fiber diameter for the location of a fiber from a nominal straight line.
In one proposed system, the opposite ends of the linear array fibers in a sensor subassembly are terminated in a manner that facilitates detection of light signals. The signals in the linear array are detected by electronic photodiodes or charge coupled devices (CCD) that are focused onto the fiber ends. According to one design, the fibers are terminated in a grid with uniform spacing that matches in accuracy the spacing of the device sites in a matrix CCD. The lens in a camera assembly that contains the CCD device focuses the CCD onto the optical fiber ends in the grid array. Scanning of each fiber is accomplished by commercially available circuitry, such as that manufactured by the Reticon Corporation.
Since the camera circuits are electronically precise and scan each fiber in sequence, the captured data is accurate in timing. However, because of the translation from linear data obtained from the document to grid data at the camera, the data at the CCD is not true in the physical spacing of the data sites.
In view of the above, it is an object of the present invention to provide a method and a system for correcting the manufacturing variations that occur in the positional alignment and spacing of optical fibers in an optical fiber scanning head.
It is another object to provide an optical fiber scanning and automatic digitizer system which permits high precision scanned data to be obtained from a relatively low precision optical fiber scanner.
It is another object to provide an optical fiber scanning and automatic digitizer system which corrects, at high speed, the manufacturing variations in the positional alignment and spacing of optical fibers of the scanner while the data is binary form.
It is another object to determine the scan head signature of an optical fiber scanning head in the form of the actual X and Y positional locations of each fiber and their variation from their nominal X and Y positions with respect to its base line caliberation positions, and to compensate for such variations to obtain acceptable performance for each fiber of the optical fiber scan head.